The present invention relates to a damping device to be utilized for a seismic base isolation system or like preventing vibration at an occurrence of an earthquake or like from being transmitted from a base structure to a building structure and for a vibration suppression system or like preventing a multistoried building from being swung itself at an occurrence of an earthquake.
In a prior art, there is known a damping device for seismic base isolation system or vibration suppression system such as shown in FIG. 6 as damping device 1, which is disclosed in Japanese Patent Laid-open Publication No. HEI 10-184757. Such damping device 1 is disposed between two object (objective) portions 2a, 2b of a building or like for damping vibration of the object portions 2a, 2b. 
With reference to FIG. 6, the damping device 1 is provided with a casing 3, a ball screw mechanism 5 for converting a linear motion between the object portions 2a and 2b to a rotational motion of a cylindrical rotation member 4 and a damping member 6 resisting the rotational motion of the rotation member 4. The ball screw mechanism 5 includes a nut 7 which is supported rotatably by the casing 3 and connected to the rotation member 4. The casing 3 has a base end 3b secured to one 2b of the object portions. The ball screw mechanism 5 includes a screw shaft 8 projecting outward from a front end portion 3a of the casing 3 and fixed to the other one 2a of the object portions.
The damping member 6 accommodates a viscous fluid 9 sealed between an inner peripheral portion of the casing 3 and an outer peripheral portion of the rotation member 4. According to such structure, the relative linear motion between the object portions 2a, 2b is converted to the rotational motion of the rotation member 4 by means of the ball screw mechanism 5, and at this time, the damping member 6 acts to resist the rotational motion of the rotation member 4.
Further, the above Japanese Publication discloses a modified damping device 11 such as shown in FIG. 7. With reference to FIG. 7, the modified damping device 11 is provided, as is similar to the damping device 1 of FIG. 6, with a casing 13, a ball screw mechanism 15 for converting a linear motion between the object portions 2a and 2b to a rotational motion of a cylindrical rotation member 14 and a damping member 16 resisting the rotational motion of the rotation member 14. In this modified damping device 11, differing from the damping device 1 of FIG. 6, a gap W is formed between the front end (lower end as viewed) portion of the cylindrical rotation member 14 and the bottom portion of the casing 13 so that viscous fluid 19 fills not only outside the rotation member 14 but also inside the rotation member 14, and the viscous fluids inside and outside the rotation member 14 are communicated with each other at the inner lower portion of the casing 13.
In the damping devices 1 and 11 of the conventional structures, in order to impart a large damping force (damping power) to the rotational member 4 (14), it is necessary to increase contacting area between the rotation member 4 (14) and the viscous fluid 9 (19). However, in the conventional damping device 1 of FIG. 6, because only the outer peripheral surface of the rotation member 4 contacts the viscous fluid 9, it is difficult to make large the damping force per unit length in the axial direction of the rotation member 4 in its axial direction. In order to obviate such defects and make large the damping force, it becomes necessary to elongate the axial length of the rotation member 4, resulting in increasing of the size of the rotation member 4, i.e., entire damping device 1, providing an inconvenience in production of the damping device.
On the other hand, in the damping device 11 of FIG. 7, since the inner and outer peripheral surfaces of the rotation member contact the viscous fluid 19, the contacting area can be made large. However, in this structure, the viscous fluid 19 inside the rotation member 14 is rotated together with the rotation member 14 when rotated, and hence, the viscous fluid 19 inside the rotation member 14 cannot be fully shared. That is, the viscous fluid 19 inside the rotation member 14 cannot perform sufficient resisting function against the rotational motion of the rotation member 14, and as a result, it becomes difficult to make large the damping force per unit length in the axial direction of the rotation member 14, thus also providing a problem.
The present invention was conceived in consideration of the above circumstances in the prior art and aims to provide a damping device capable of making large a damping force per unit length of the damping device in its axial direction.
Hereunder, the present invention will be explained. Further, the description is made by adding reference numerals in the accompanying drawings for the sake of easy understanding of the present invention, but the present invention is not limited to the shown embodiment.
In order to achieve the above object, the inventors of the subject application provide a damping device (20, 50) for substantially preventing vibration from transmitting or causing between two object portions which comprises a motion conversion section (21) for converting a relative linear motion between object portions to a rotational motion of a rotation member (30) and a damping section (22) resisting the rotational motion of the rotation member (30), wherein the damping section (22) is provided with an inner peripheral side sealing layer (34) disposed on an inner peripheral side of the rotation member (30) and an outer peripheral side sealing layer (33) disposed on an outer peripheral side of the rotation member, the inner peripheral side sealing layer (34) and the outer peripheral side sealing layer (33) being sealed with viscous medium so as to achieve a resisting function against the rotational motion of the rotation member (30). Further, in this aspect, as the motion conversion section, various mechanisms may be utilized as far as they can convert the linear motion to the rotational motion, and for example, ball screw mechanism, screw mechanism having a lead and a rack/pinion mechanism may be utilized.
According to the subject feature of the present invention mentioned above, since the inner peripheral side sealing layer and the outer peripheral side sealing layer contact the rotation member, while resisting the rotational motion of the rotation member, the damping force per unit length of the rotation member in its axial direction can be made large. Further, in the case where a damping force is needed approximately corresponding to that in the conventional damping device, the axial length of the rotation member can be reduced in substantially half length, thus making compact the entire structure of the rotation member, i.e., damping device, in addition to easy manufacturing thereof.
The present invention is further characterized in that the damping section (22) is further provided with an outer cylindrical member (31) disposed outside the rotation member (30) and an inner cylindrical member (32) disposed inside the rotation member (30) and secured to the outer cylindrical member (31), the outer peripheral side sealing layer (33) is arranged between the outer cylindrical member (31) and the rotation member (30) and the inner peripheral side sealing layer (34) is arranged between the rotation member (30) and the inner cylindrical member (32), the inner and outer peripheral side sealing layers (34) and (33) being sectioned from each other.
According to the invention of this aspect, the inner peripheral side sealing layer and the outer peripheral side sealing layer are shared, so that the sealing layers can surely resist the rotational motion of the rotation member. For this reason, the damping force per unit length of the rotation member in its axial direction can be made large. In a case where the inner peripheral side sealing layer and the outer peripheral side sealing layer are communicated with each other, both the layers may adversely influence each other to act to weaken the damping force to the rotation member.
Furthermore, the present invention is characterized in that the rotation member (30) is supported by the outer cylindrical member (31) and the inner cylindrical member (32) through support means (37, 37, 38, 38). Bearings such as usual bearings, sliding bearings or like may be utilized.
As the factors for influencing the damping force, in addition to the contact area between the viscous fluid and the rotation member 30 as mentioned above, there will be listed up a gap between the rotation member and the outer cylindrical member and a gap between the rotation member and the inner cylindrical member, i.e., the thickness of the sealing layer. As the damping force is in reverse proportion to the thickness of the sealing layer, in order to make large the damping force, it is necessary to reduce the thickness of such sealing layer. In this regard, according to the present invention, since the rotation member is supported by the outer cylindrical member and the inner cylindrical member through supporting means such as radial bearings, respectively, the rotation member is free from the collision with the outer and inner cylindrical members even in the case of small gaps between the rotation member and the outer and inner cylindrical members, respectively. As a result, these gaps can be easily controlled, and moreover, the thickness of the sealing layers can be made small so as to make large the damping force per unit length in the axial direction of the rotation member.
Still furthermore, the present invention is characterized in that the motion conversion section (21) is provided with a casing (24) connected to the outer cylindrical member (31), a nut member (25) supported to be rotatable by the casing (24) through a support structure and a screw shaft (26) screwed with the nut member (25), and the rotation member (30) is coupled with the nut member (25).
Further, in the case where the screw mechanism is utilized for the motion conversion means, there is a tendency of increasing the axial length of the damping device due to the screw shaft. According to the present invention, however, since the axial length of the rotation member can be made short, the elongation of the axial length of the damping device can be suppressed even in the utilization of the screw mechanism.